This invention relates generally to imaging systems capable of operation in multiple modalities, and more particularly to methods and systems for controlling the operation of multi-modality systems.
Multi-modality imaging systems are capable of scanning using different modalities, such as, for example, Positron Emission Tomography (PET), Single Positron emission tomography (SPECT), Computed Tomography (CT), Static X-Ray imaging, and Dynamic (Fluoroscopy) X-Ray imaging. In a multi-modality system (also referred to as a multi-modal system), a portion of the same hardware is utilized to perform different scans (e.g., an image produced by SPECT is processed and displayed respectively, by the same computer and display, as an image produced by CT). However, the data acquisition systems (also referred to as an imaging assembly) are different. For example, on a CT/SPECT system, a radiation source and a radiation detector are used in combination to acquire CT data, while a radiopharmaceutical is typically employed in combination with a SPECT camera to acquire SPECT data.
In multi-modality systems, such as, for example, an integrated SPECT/CT system, a single detector may be used to receive transmission image data in the form of x-ray photons and emission image data in the form of gamma ray photons. At least some known multi-modality systems attempt to detect and process image data from each different modality simultaneously. This method attempts to reduce imaging scan time by collecting and processing data from each modality simultaneously. However, the reduction realized by detecting and processing images from different modalities simultaneously may be only minimal because an emission scan typically takes several minutes, for example, approximately twenty minutes, and a transmission scan typically takes only several seconds, for example, approximately fifteen seconds.
During an emission portion of a scan, the multi-modality system detects and counts individual emission gamma photons at a relatively low rate, such as, only a few photons per pixel per second, and processes the gamma ray photons to determine an energy level of each gamma ray photon. During a transmission portion of a scan, the multi-modality system may operate a source of x-ray photons, such as an x-ray tube. The detector may be exposed to a relatively high x-ray photon flux from the x-ray source. However, a multi-modality system that attempts to perform an emission portion of the scan and the transmission portion of the scan simultaneously may receive x-ray photons at such a rate that signal conditioning electronics within the system cannot discriminate each x-ray photon received and may saturate or otherwise be damaged by the relatively high rate at which the x-ray photons are received.